This invention relates generally to media handling for inkjet printing systems.
An inkjet printing mechanism is a type of non-impact printing device which forms characters, symbols, graphics or other images by controllably spraying drops of ink. The mechanism typically includes a cartridge, often called a xe2x80x9cpen,xe2x80x9d which houses a printhead. There are various forms of inkjet printheads, known to those skilled in the art, including, for example, thermal inkjet printheads and piezoelectric printheads. The printhead has very small nozzles through which the ink drops are ejected. To print an image the pen is propelled back and forth across a media sheet, while the ink drops are ejected from the printhead in a controlled pattern. Other inkjet printing mechanisms employ a stationary printhead which spans the entire print-zone, and hence are known as a page-wide-array printhead or a print bar. Inkjet printing mechanisms may be employed in a variety of printing systems, such as printers, plotters, scanners, facsimile machines, copiers, and the like.
Typically inkjet printing systems include a roller for feeding a media sheet along a media path. Curling of the media sheet sometimes occurs due to rapid environmental changes and ink deposition. The printer heater for example contributes to the environmental changes. Curling occurs across the media sheet and also along the length of the media sheet. One challenge is that the media sheet may curl within the print-zone adversely affecting print quality. It is particularly undesirable for the media sheet to curl into contact with the printhead where damage can occur to the media, the printed image, the printhead or the print system. One solution is to increase the spacing between the pen and the media to reduce the likelihood of printhead contact. However, with a varying or higher xe2x80x9cpen to paperxe2x80x9d spacing (xe2x80x9cPPSxe2x80x9d) along the media sheet, print quality is reduced. It is preferred that xe2x80x9cpen to paperxe2x80x9d spacing remain constant along the various portions of the media sheet passing through the print-zone.
In an inkjet printing apparatus an inkjet printhead ejects ink into a print-zone. A drive shaft, located upstream of the printhead, has a longitudinal axis, a first radius over a central length, and a second radius less than the first radius at a first recess and a second recess. Each recess is peripheral to the central length. A plurality of pinch devices stabilize the media against the drive shaft. A first guide and a second guide, spaced from the longitudinal axis, are aligned with and extend into the first recess and second recess.